Objective: Major depressive disorder (MDD) and chronic non-cancer pain conditions (CNPC) often co-occur and exacerbate one another. Treatment-resistant depression (TRD) in adults with CNPC can amplify the economic burden. This study examined the impact of TRD on direct total and MDD-related healthcare resource utilization (HRU) and costs among commercially insured patients with CNPC and MDD in the US. Methods: The retrospective longitudinal cohort study employed a claims-based algorithm to identify adults with TRD from a US claims database (January 2007 to June 2017). Costs (2018 US$) and HRU were compared between patients with and without TRD over a 12-month period after TRD/non-TRD index date. Counterfactual recycled predictions from generalized linear models were used to examine associations between TRD and annual HRU and costs. Post-regression linear decomposition identified differences in patient-level factors between TRD and non-TRD groups that contributed to the excess economic burden of TRD. Results: Of the 21,180 adults with CNPC and MDD, 10.1% were identified as having TRD. TRD patients had significantly higher HRU, translating into higher average total costs (US$21,015TRD vs US$14,712No TRD) and MDD-related costs (US$1201TRD vs US$471No TRD) compared with non-TRD patients (all p < 0.001). Prescription drug costs accounted for 37.6% and inpatient services for 30.7% of the excess total healthcare costs among TRD patients. TRD patients had a significantly higher number of inpatient (incidence rate ratio [IRR] 1.30, 95% CI 1.14–1.47) and emergency room visits (IRR 1.21, 95% CI 1.10–1.34) than non-TRD patients. Overall, 46% of the excess total costs were explained by differences in patient-level characteristics such as polypharmacy, number of CNPC, anxiety, sleep, and substance use disorders between the TRD and non-TRD groups. Conclusion: TRD poses a substantial direct economic burden for adults with CNPC and MDD. Excess healthcare costs may potentially be reduced by providing timely interventions for several modifiable risk factors.